1. Field of the Invention
The present invention relates to a high-frequency power amplifier having differential inputs, and more specifically to a high-frequency power amplifier having differential inputs, capable of simplifying a structure of an output port of a communication system for 2.4 GHz ISM frequency band by designing and producing a high-frequency power amplifier having differential inputs for 2.4 GHz ISM frequency band using a silicon germanium (SiGe) microwave monolithic integrated circuit (MMIC).
2. Background of the Invention
FIG. 1 is a constructional view showing an output port of a conventional communication system.
As shown in FIG. 1, a high-frequency transmission unit 10 of a conventional communication system has two output terminals. The signals output from the two output terminals are have phases inverted each other, and this output is referred to as “a balance output”.
On the other hand, a conventional power amplifier 30 for amplifying and sending a signal to an antenna 40 has one input terminal and one output terminal. Therefore, a signal, which can be received by the conventional power amplifier 30, is so called “an unbalance signal”. The unbalance signal means a signal not having a phase inverted from other signals.
Therefore, in order to amplify the signals output from a high-frequency transmission unit and send the amplified signals to the antenna, a signal conversion unit 20 for converting the balance signal into the unbalance signal and sending the unbalanced signal to an output amplifier is required. Generally, a balanced-to-unbalanced element (e.g. a BALUN element) which is a passive element is used as the signal conversion unit 20.
Accordingly, in the conventional power amplifier 30, there is a problem that the input signal is attenuated due to a characteristic of the BALUN element used in signal conversion.
Therefore, in the conventional power amplifier 30, the signal attenuated due to the BALUN element must be compensated to satisfy an output power of the antenna 40 required for the communication system. In other word, there is a problem that a power gain required for the power amplifier is increased.